1. Field of the Invention
The present invention relates to a variable bulge device for a rotation head drum, capable of being used in video cassette recorders, digital audio tape recorders and camcorders, and more particularly to such a device capable of adjusting a protruded amount of a bulge, depending on a rotation speed of the rotating head drum and the kind of a tape used.
2. Description of the Prior Art
In a magnetic recording and reproducing apparatus including a rotation head device, a tape T is partially wound around upper and lower drums 1a and 1b of the rotation head device. During travel of the tape T, a rotation head 3 of the rotation head device performs a recording operation and a reproducing operation. When the rotation head 3 comes into contact with the tape T or moves away from the tape T, a slight vibration is generated from the tape T. This vibration results in error generated by lapse of time and so called impact error. By such an impact error, a picture distortion of reproduced image may be generated which results in a degradation in picture quality. The impact error is more severely generated when the rotation head 3 moves away from the tape T, over the case when the rotation head 3 comes into contact with the tape T.
There has been known means for reducing such an impact error. For example, as shown in FIGS. 2A and 2B protrusions (namely, bulges) 4a and 4b are slightly protruded beyond a travel path of the tape T from upper portions of the fixed lower drum 1b of the rotation head device near tape inlet and tape outlet portions, respectively,
The bulges 4a and 4b serve to inhibit an abrupt deformation of the tape T into a tent shape when the rotation head 3 comes into contact with the tape T and moves away from the tape T, The bulges 4a and 4b also inhibit a longitudinal vibration of the tape T and reduces an impact error generated from the tape T,
At a position near the tape inlet portions of the fixed lower drum 1b and the rotating upper drum 1a, the tape T is wound around the upper drum 1a above the rotation head 3, as shown in FIG. 2A. Accordingly, the tape T is radially spaced from the peripheral surface of the upper drum 1a. However, the radial space of the tape T is smaller than the thickness of the bulge 4a. As a result, it is difficult to inhibit the lateral vibration of the tape T and thereby to effectively reduce the impact error. At a position near the outlet portions of the fixed lower drum 1b and the rotating upper drum 1a, the portion of the tape T disposed above the rotation head 3 is wound around the upper drum 1a, as shown in FIG. 2B. However, little air film is present between the tape portion and the upper drum 1a. As a result, the upper edge of the tape T vibrates severely in lateral direction. Due to such a vibration, it is difficult to effectively reduce the impact error.